Apparatus for supplying charge material to mass spectrometers



Nov. 18, 1952 v. L. PARSEGIAN ET AL 2,618,750

APPARATUS FOR SUPPLYING CHARGE MATERIAL TO MASS SPECTROMETERS Filed Oct. 6, 1950 4 Sheefcs-Sheet l INVENTOR.

VOZCAN LAWRENCE PARSEGMN CHARLES M- 5TEVENS 1952 v. 1.. PARSEGIAN ETAL 2,618,750

APPARATUS FOR SUPPLYING CHARGE MATERIAL TO MASS SPECTROMETERS Filed Oct. 6, 1950 4 Sheets-Sheet 2 INVENTOR.

VOZCAN- LAWRENCE PARSEGlAN CHARLES M, STEVENS B YflM/QM 1952 v. L. PARSEGIAN ETAL 8,750

APPARATUS FOR SUPPLYING CHARGE MATERIAL TO'MASS SPECTROMETERS Filed OGC. 6, 1950 4 Sheets-Sheet 3 M w R GS m mm N AV E PE V 2.3 N C I. N..

K Ms E mm mm/ w Y v'. PARSEGIAN ET AL Nov. 18, 1952 I APPARATUS FOR SUPPLYING CHARGE MATERIAL. TO MASS SPECTROMETERS Filed 001;. 6, 1950 4 Sheets-Sheet 4 FIG.7.

IN V EN TOR.

VOZCAN LAWRENCE PAESEQAN CHARLES M.$TEVEN5 Patented Nov. 18, 1952 APPARATUS FOR SUPPLYING CHARGE MATERIAL T MASS SPEOTROMETERS Vozcan Lawrence Parsegian, Brooklyn, N. Y and Charles M. Stevens, Chicago, Ill., assignors to the United. States of America as represented by the United States Atomic Energy Commission Application October 6, 1950, Serial No. 188,824

12 Claims.

This invention relates to the art of-mass spectrometry and more particularly to a new and improved apparatus formoving materials into the analyzer chamber or tube of mass spectrometers. Whereas many arrangements for passing materials in gaseous forminto the ionizing zone of the mass spectrometer have been devised and some arrangements for moving materials in liquid or solidform into the ionizing zone have been suggested, nevertheless so faras known each of the latter arrangements have had certain inherent disadvantages which it is a purpose of the present invention to overcome. For example, the introduction of a charge of solid samples into the analyzer tube of spectrometers, either as a single sample or as a plurality of samples introduced simultaneously, necessitates the breaking of the vacuum in the tube during the insertion of such sample, then the comparatively slow and expensive reestablishment of that vacuum followed by the reestablishment of the electrical conditions employed during the analysis of the sample.

The present invention on the contrary has as an object the provision of a rapid and economical means for introducing'non-gaseous samples into an evacuated interior of a massspectrometer.

A second object is to provide a new combination of a mass spectrometer and a means for introducing materials thereto without interrupting the vacuum of the spectrometer.

A third object is to provide a new and improved vacuum lock system.

Another object is to provide a new and improved vacuum sealing means.

Another object is to provide an improved evacu- I ating means for a mass spectrometer.

Still another object is to provide a continuous loading means for mass spectrometers.

A further object is to provide an intermittent loading means for mass spectrometers.

Other objects and advantages of our invention will become more apparent as the description proceeds; when considered in conjunction with the accompanying drawings in which,

Figure 1 is a diagrammatic view, partly in section, showing one arrangement for continuously supplying charge material to an analyzing apparatus;

Figure 2 is a detail View showing one arrangement for passing a tape conveyor through a vacuum system housing;

Figure 3 is a diagrammatic view partly in section, showing a second arrangement in operative position for supplying charge material to an analyzing apparatus;

Figure 4 is a partial view of the arrangement showninFigure 3 with the probe element in withdrawn position;

Figure 5 is a detail of one end of the probe showing one arrangement of the probe with respect to interior elements of a conventional mass spectrometer analyzer tube;

Figure 6 is a diagrammatic View showing one arrangement for passing a tape conveyorthrough the ionizing region of a mass spectrometer analyzer tube;

Figure '7 is another diagrammatic view of the arrangement depicted in Figure 6, but serving as a side viey of such arrangement; and

Figures 8, 9 and 10 are enlarged detail views showing one arrangement for moving the tape into and out of the evacuated analyzer tube.

Referring first to Figure 1, a preferred. arrangement is shown wherein materials in non-gaseous form, such as solids or liquids, may be continuously introduced into a mass spectrometer in accordance with our invention. By means thereof it is possible to provide a continuous analysis of non-gaseous material for control or monitoring of an industrial process, as will be apparent to those skilled in the art. As shown, a conventional mass spectrometer having an analyzer tube It, magnet H and collector means I2 is provided with the usual preamplifier l3, amplifier l4 and suitable recording means l5. Attached to said tube at a suitable location is a housing 20 for a vacuum lock system and which housing may be supported and insulated in any convenient manner, not shown. Extending lengthwise through said housing from the exposed outer end thereof to the inner end communicating with the analyzer tube ii) is located one or more passages 21 and 22 relatively small in cross section and serving a purpose later to be described. Contained within said housing and in communication with said passages is a plurality of vacuum spaces or chambers, here shown as 23, 24 and 25, adapted to be maintained at progressively greater degrees of evacuation as the passages approach the analyzer tube of the mass spectrometer.

In order to establish and maintain satisfactory vacuum conditions within the housing and analyzer tube, the improved arrangement of a vacuum lock assembly or system comprising the p i e n an va u m n ic tin m a shown in Figure 1 has been found to be suitable when operating the spectrometer analyzer tube with vacuums in the ranges of 2.4 x lo mm. Hg o 1-0 X 10 mm- Ha. n such ases a com vent-ional mechanical pump indicated generally at 26 serves to reduce the pressure of chamber 23 to within the range of 2.2 to mm. Hg and this condition may be observed by means of a conventional manometer 21. A second and separate mechanical pump 28 serving as a backing pump for the exhaust of a second diffusion pump 22 connected to chamber 24 serves to reduce the pressure of that chamber to within the range of 2.0 to 0.0 microns I-Ig. In turn, the pressure existing within that chamber may be observed by means of a Pirani type gage indicated generally at 30.

Through a first diffusion pump 3| exhausting into the high vacuum side of the second diffusion pump 29 and connected to chamber 25 the pressure within that chamber in turn may be reduced to within the range of 2.4 x 10- mm. Hg to 1.0 X 10- Hg. As will be apparent, the pressure existing in chamber 25 may optionally be the pressure used in the analyzer tube E0 or if desired may be the pressure of a bufier stage ahead of that tube if the conventional vacuum means of the mass spectrometer is also to be employed. For the purpose of observing the pressure in chamber 25 an ion gage indicated generally at 32 may be employed.

With the structural arrangement as thus described, a suitable flexible conveying means, preferably in the form of a tape 40 which can withstand the heating efiect required for the ionization of the non-gaseous material carried thereby is provided for movement into the analyzer tube through passage 2| and for movement from that tube through passage 22. Such tape Or ribbon may be made of tantalum, tungsten, nichrome or similar material wound upon spool 4| and may have any suitable configuration on its exposed side, such as spaced grooves or the like, suitable for holding non-gaseous material. A second tape 42 wound upon spool 43 serves to provide a protecting layer for tape 40, as well as serving a sealing function, and is brought into contact with the conveying tape prior to entry into housing 20, is separated from tape 40 while within the analyzer tube as best shown in Figures 8 to 10 and is brought out of housing 20 in contact with tape 40, whereupon both tapes are wound upon a third spool 44.

As indicated in Figure 2 the tapes are so dimensioned and arranged that they provide a substantially tight seal for the respective passages 2! and 22 through which they are adapted to move. In one satisfactory arrangement it was found that metal tapes each having a width of 0.097 inch and a thickness of 0.0063 inch could be moved through a passage of 0.100 inch width and 0.015 inch thickness at a rate of about one inch per second while the vacuum system was in operation within the desired range of pressures. As will thus be seen, the clearance of such tapes within the passages approaches capillary dimen- SlOIlS.

Referring now to Figure 8, as the respective tapes approach the entrance to the analyzer tube In through passage 2| and into the hollow end of housing 20 the cover tape 42 is directed upon a freely revolving roller 50, passes across a second roller offset from the plane of roller 59 and thence across a third roller 52 set in the plane of roller 50 whereupon the direction of travel of such tape is reversed and it then may pass outwardly through passage 22. By this arrangement of tape travel the tape 40 carrying the non-gaseous material to be analyzed then moves in an exposed condition around roller 54 and across rollers 56 and 51 in the path of any suitable ionizing means employed in the conventional ionizing source region of the mass spectrometer. Such tape then moves around roller 55 and passes outwardly through passage 22 with the cover tape 42 whereupon both tapes may then be wound upon spool 44 exteriorly of the apparatus. A suitable cantilever supporting framework disposed within the open end of housing 243 and within the tube I0 provides for the necessary mounting of the several parts and forms no essential part of our invention. As will be apparent to those skilled in the art the housing 29 may if desired be mounted along the axis of analyzer tube it), rather than perpendicular thereto as shown in Figure 1.

While any suitable mass spectrometer ionizing means may be used in connection with our invention, the arrangement shown diagrammatically in Figures 6 and 7 may be employed if desired with satisfactory results. For example, tape 49 moving across direction changing idler rollers 54 and 55 and supporting rollers 56 and 5'! may pass under a shield 60, shown in Figures 6 and '7, maintained at a positive voltage somewhat lower than the voltage of the tape itself and may be subjected to a copious electron bombardment from. a pair of spaced filaments BI and 62 under the shield and supported in suitable insulator stems 63 and 64. Positive ions formed from the material under bombardment on tape 40 are drawn through collimating slits in grounded plates 65 and 66 are centered as a beam by an electrode 6! maintained at a small positive potential. This beam after passing the slit in plate 66 then is directed through the analyzer tube 10 in the cu"- tomary manner.

In operation of the modification of our invention thus far described, a material to be analyzed, such as a continuously flowing radio-active solu-- tion in a, plant process including conduit 10, may be drawn through a pipe H in a shielding wall 72 by means of pump 13 and deposited by dispensing means M upon the moving tape 40. Excess solution may be returned to the conduit through a second pipe 15. If it is desired to provide a solid rather than a liquid deposit upon such tape, any suitable drying means, not shown, may be provided intermediate spools 4| and 43. Furthermore, if desired a separate degassing heater l6 may be disposed in the vacuum chamber 25 to remove absorbed gases from the metal tapes, or even for a preliminary decomposition of sample material on tape 40, which material may normally evolve large volumes of gas at elevated temperatures and which should be substantially prevented from being evolved within the spectrometer tube.

Whereas the continuous introduction of materials as thus described embodies a preferred form of our invention, the invention in its broader aspects contemplates also the intermittent introduction of non-gaseous materials to the analyzer tube. For example as shown in Fig. 3, one means for intermittently introducing nongaseous materials into a mass spectrometer analyzer tube While embodying certain major advantages of our invention is shown. Axially disposed of the analyzer tube H0 is a housing E20 having a centrally disposed axial aperture [2| adapted to receive a movable hollow probe means Hi0.

Housing is provided with vacuum spaces 23, [24 and I25 to which is normally connected the vacuum producing arrangement of mechanical and diffusion pumps hereinabove described with respect to Figure 1. In addition, at the outer end of the housing and surrounding the same, an apertured framework we is attached. The end of the housing preferably supports a threaded gland It! by means of which an additional seal for the movable probe may be employed whenever desired and at the extreme outer end of framework IIlfl is located a shoulder I02 against which positioning collar I83 on the probe may abut and which may be held in the proper position thereagainst by atmospheric pressure Since withdrawal of probe M for reloading would necessarily adversely affect the vacuum stability of the system, means are provided for sealing each of Vacuum chambers I24 and I23 in turn as the probe is withdrawn and for reopening the same in inverse order as the probe is reinserted. One convenient means for accomplishing this may comprise a rigid control rod IM aifixed to probe HIE] exteriorly of housing I29 and adapted to move simultaneously with said probe. Preferably rod I84 is slightly longer than its companion probe and is provided with a forward projecting cam surface I65. Rod IM may be guided by means of suitable stationary brackets I06, I91 and I08 respectively, mounted upon the framework and housing.

Also mounted by suitable stationary supports upon the housing above vacuum spaces I23 and I24 are sealed bellows type valve housings I26 and I2! adapted to be moved in one direction by the mechanical camming action of the control rod IM and to move in the other direction by atmospheric pressure. At the top of said valve housings guide brackets I28 and I29 are located and within the housings suitable gate type valves I30 and I3I are positioned for coaction with appropriate valve seats in vacuum spaces I23 and As shown in Figures 3 and l, one form of ionizing means, suitable for thermionic emission of the material to be analyzed, is disposed at the end of tube H0 although it will be understood that any other conventional mass spectrometer ionizing means may be used without departing from our invention. The hollow probe Mt preferably contains an electrical circuit, insulated from said probe, by means of which a charge previously deposited upon a wound filament I50 may be heated to emission temperature. Within the tube III) a grounded support having a pair of collimating plates I5I and IE2 with slits therein is mounted in operative relation to said filament when the collar I03 thereof is abutting the shoulder IE2 of the vacuum housing. Ion focus electrodes I53 within the tube may simultaneously be maintained at a positive potential somewhat higher than the positive potential of the filament while beam deflector plates I54 may be maintained at a potential slightly above ground.

With the arrangement as thus described the probe with a charge in place upon the filament may readily be inserted into the apparatus while the vacuum system and the mass spectrometer are in operative adjustment and thereafter by applying an electrical current to said filament the material thereon may be subjected to thermionic emission and ions therefrom directed through the tube IIil. After this charge is analyzed the probe can be quickly Withdrawn, the vacuum system meanwhile remainin operative since the valves close behind the withdrawn probe, as shown in Figure 4. After being reloaded with the next charge the probe can be quickly replaced in its former operative position and the next charge can be analyzed without delay incident to reestablishing a vacuum. While the above disclosure of our invention has been directed to an embodiment in which a mass spectrometer is employed, it will be apparent to those skilled in the art that the invention is not limited in its broader aspects to use with this sole type of apparatus. For example, it may be equivalently employed in connection with electron microscopes in which a sample of material is to be introduced into an evacuated chamber and subjected to an electron bombardment. Moreover, it is contemplated that certain features of our invention such as the vacuum lock may be used when desired in connection with vacuum furnaces or other evacuated structures into which non-gaseous materials are to be introduced.

Accordingly, the foregoing description while representative of a preferred use of the invention, is nevertheless to be interpreted in an illustrative rather than a limiting sense. It is intended that the boundaries of the invention should be limited only in accordance with the scope of the claims appended hereto.

We claim:

1. In combination, a mass spectrometer having an analyzer tube adapted to remain in evacuated condition during supply of material thereto, a vacuum housing containing at least three vacuum spaces maintained at separate subatmospheric pressures, a passage extending through said housing and spaces and terminatin at one end in the tube and at the other end in the atmosphere surrounding said housing, chargetransporting means movable through said passage adapted substantially to seal the same and to transport a non-gaseous material into said tube and pressure retaining means in contact with said transporting means adjacent the atmospheric end of said passage thereby to assist in said sealing action.

2. Charge loading means for a mass spectrometer including a vacuum lock assembly, a hollow probe adapted to be reciprocated through said assembly, sample retaining means mounted at one end of said probe and adapted to be heated, and heating connections extending through said probe from said sample retaining means to an external electrical circuit.

3. Charge loading means for a mass spectrometer including a vacuum lock assembly, a tape adapted to be moved seriatim from a loading point externally of the assembly, through said assembly into the spectrometer and from the spectrometer through the assembly to a point externally of the assembly, and means for loading upon said tape a charge of material to be analyzed within said spectrometer.

4. Apparatus as defined in claim 1, wherein said pressure retaining means comprises a movable tape adapted to contact said charge transporting means.

5. Apparatus as defined in claim 1, wherein said pressure retaining means comprises a gland seal adapted to contact said charge transporting means.

6. A vacuum system for use with a mass spectrometer including a housing attached to said spectrometer, a passage for receiving a charge loading means and extending from the atmosphere through said housing into said spectrometer, a first chamber within said housing communicating through said. passage with the atmosphere and adapted to be maintained at at pressure of about 0 to 3 mm. Hg, a first evacuating means connected to said first chamber, a second chamber within said housing communicating through said passage with said first chamber and adapted to be maintained at a pressure of about 0 to 2 microns, a second evacuating means connected to said second chamber, a third chamber within said housing communicating through said passage with said second chamber and with the analyzer tube of said spectrometer and adapted to be maintained at a pressure of about 1 x 10- mm. Hg to 3 x 10- mm. Hg, and

a third evacuating means connected to said third chamber.

7. Apparatus as described in claim 6 having heating means disposed within said third chamber whereby material moving through said passage into said spectrometer may be degassed.

8. Apparatus as described in claim 6 having externally actuated valve means mounted upon said housing for selective closing of the passage between said second and third chambers and between said first chamber and the atmosphere.

9. Charge loading means for :a mass spectrometer including a vacuum lock assembly having a plurality of communicating vacuum spaces, a hollow probe adapted to be reciprocated through said assembly, charge loading means mounted at one end of said probe and-adapted to be heated, heating connections extending from said charge retaining means to an external electrical circuit, and valve means adapted to close communication between said vacuum spaces following withdrawal of said probe from said assembly.

10. Apparatus as described in claim 9, wherein said valve means is actuated by said probe.

11. Charge loading means for a mass spectrometer including a vacuum lock assembly having a plurality of communicating vacuum spaces, a hollow probe adapted to be reciprocated through said assembly, charge loading means mounted at one end of said probe and adapted to be heated, heating connections extending from said charge retaining means to an external electrical circuit, and valve means adapted to open communication between said vacuum spaces upon insertion of said probe into said assembly.

12. Apparatus as described in claim 11, wherein said valve means is actuated by said probe. VOZCAN LAWRENCE PARSEGIAN. CHARLES M. STEVENS.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Lock in Review of Scientific Instruments, volume 12, September 1941, page 450. 

